1. Field of the Invention
The invention presently described relates to the analysis of a component in a test sample whereby a reactant system interacts with the component to produce a detectable response indicative of the presence and/or concentration of the component. More particularly, the invention relates to a carrier matrix comprised of separate filaments formed into a cloth, in which some of the filaments are incorporated with at least one ingredient of the reactant system prior to being formed into the matrix.
2. Discussion of the Prior Art
There are many test devices presently in use, especially in the medical diagnostic area, which can detect the presence of a particular component in a test sample. Besides the numerous electronic and mechanical devices useful for this purpose, one particular type of visual detection has achieved widespread recognition in the art. Thus, the so called "dip-and-read" reagent strips enjoy wide use, especially in the chemical analysis of biological fluids, because of their relative low cost, facility in use, and speed in obtaining results. Such reagent strips generally employ reactant systems impregnated in a bibulous carrier such as paper.
The bibulous carrier has taken on many forms in the prior art. For example, U.S. Pat. No. 3,846,247 teaches the use of felt, porous ceramic strips, and woven or matted glass fibers. As substitutes for paper, U.S. Pat. No. 3,552,928 teaches the use of wood sticks, cloth, sponge material, and argillaceous substances. The use of synthetic resin fleeces and glass fiber felts in place of paper is suggested in British Pat. No. 1,369,139. Another British Pat. No. 1,349,623, suggests the use of a light-permeable meshwork of thin filaments as a cover for an underlying paper matrix. This reference also suggests impregnating the paper with part of the reactant system and impregnating the meshwork with other, potentially incompatible reagents. Finally, French Pat. No. 2,170,397 teaches the use of carrier matrices having greater than 50% polyamide fibers therein.
In all of the foregoing disclosures, the reactant system (i.e., the reagents which detect the unknown component) is homogeneously impregnated into a finished matrix. Hence, in the case of cloth or woven matrices, felts, and fleeces, the ingredients of the reactant system are impregnated into the finished cloth, usually by immersion in a solution followed by drying.
Several disadvantages exist with the prior art to which the present application addresses itself. Some of the prior art devices satisfy and eliminate some of these, but none has yet been devised which jettisons them all.
One of the problems incurred by skilled artisans in the area of diagnostic test strips is that of separating mutually incompatible ingredients of a reactant system. For example, in the case of a reactant system useful in detecting occult blood in urine, it has been found that organic peroxides in the presence of an indicator such as o-tolidine will produce discoloration after long periods of storage. Another example of incompatible reagents is in the case of test strips sensitive to ketone levels in urine. In this case, the nitroprusside indicator and alkaline buffer are potentially mutually reactive. Hence, a carrier matrix capable of physically separating these ingredients from one another would be most desirable, and would greatly elevate the current state of the art.
Another void which has existed in the art is a convenient way of making a reagent strip self-calibrated. In current usage, a test strip is immersed in a urine sample and the technician must wait a predetermined time before comparing the strip with a standardized chart. The color chip on the chart which is closest to the color appearing on the test strip during the predetermined time range is indicative of the level of the component present in the system. There are many inherent disadvantages with such a procedure. Firstly, if the strip is read too late or too soon an incorrect result will ensue. Secondly, the technician reading such a strip must possess good color acuity. Even slight color blindness can cause severe inaccuracy. Thirdly, studies have shown that the results of a color comparison between a moistened strip and a standard color chart will vary somewhat from individual to individual.
The solution to this problem is a reagent strip which can be read directly without the need of recourse to an ancillary standard color chart. Thus, a strip which would read out some number or geometrical symbol indicative of the concentration of a component present in the test sample would greatly enhance accuracy and convenience of use.
Another problem encountered in reagent strips comes from the manufacturing area. Because of the great importance of accuracy in the area of analytical chemistry, it is important for manufacturers of reagent strips to keep a close watch on the quality of their products. Indeed, millions of dollars are spent each year in quality assurance programs. Products are analyzed as they leave the manufacturing area and both the stability and performance characteristics are kept under careful scrutiny. When faulty products are discovered, they are most often discarded in their entirety, thereby wasting all of the components of a particular reagent system. Surely, the state of the art would be markedly advanced if it were to become unnecessary to discard an entire batch of faulty reagent strips (and the costly reagent systems incorporated with them).
In order to address these inadequacies of the prior art, an extensive program of research and development was engaged in. A way was sought to easily separate reagents within a carrier matrix, to provide for long-term storage, to obtain better control over reagent uniformity over the entire area of a carrier matrix, and to provide a way of obtaining reagent strips which are self-calibrated. The oeuvre of these efforts is the present invention which provides a solution to each of the foregoing research goals.